Engineers have recognized that reductions in NOx emissions and combustion noise can be achieved during some engine operating conditions by slowing the initial rate of injection into the combustion chamber. Thus, it is desirable that a fuel injector have the ability to extend the time duration over which the injection goes from zero to its maximum. Although it is settled that combustion noise and NOx emissions can be reduced by slowing the initial injection rate build up, there remains considerable debate as to what initial injection rate profile achieves the best reductions in noise and emissions.
In the case of hydraulically actuated fuel injectors, initial rate shaping has been successfully introduced by spilling fuel to a return line instead of out of the nozzle during the initial portion of each injection event. The initial injection rate is reduced by allowing a significant amount of controlled fuel spillage through a plunger groove and/or holes in a barrel port. This spillage concept has been an effective front end rate shaping method, providing a significant amount of combustion noise reduction (.about.9 dB) and achieving significant overall engine noise reduction (.about.3 dB).
The present invention is directed as an alternative to the fuel spillage concept as it relates to producing initial injection rate shaping to reduce NOx emissions and combustion noise.